Communication apparatus and communication method

ABSTRACT

[Object] To provide a communication apparatus and a communication method which are capable of reducing the overhead of communication while suppressing influence on the frame reception process. 
     [Solution] Provided is a communication apparatus, including: a processing unit configured to select one of a frame of a first format including a training signal and a frame of a second format not including a first field which is at least a part of the training signal, and generate the frame of the selected format; and a communication unit configured to transmit the frame of the first format or the frame of the second format. Also provided is a communication method, including: selecting one of a frame of a first format including a training signal and a frame of a second format not including a first field which is at least a part of the training signal, and generating the frame of the selected format; and transmitting the frame of the first format or the frame of the second format.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15/508,803, filed Mar. 3, 2017, which is based on PCT filingPCT/JP2015/072072, filed on 4 Aug. 2015, and claims priority to JapanesePatent Application No. 2014-223538, filed on Oct. 31, 2014, the entirecontents of each are incorporated herein by its reference.

TECHNICAL FIELD

The present disclosure relates to communication apparatuses andcommunication methods.

BACKGROUND ART

Wireless local area networks (LANs), typified by IEEE (Institute ofElectrical and Electronics Engineers) 802.11, have in recent years beenwidespread.

802.11 is a random access type wireless communication standard, and in802.11, when a plurality of communication apparatuses performtransmission asynchronously, a mechanism such as carrier sense multipleaccess (CSMA)/collision avoidance (CA) is employed to suppress adecrease in throughput of communication due to collision of transmissionpackets. Specifically, a communication apparatus conforming to 802.11checks a state of a channel before performing packet transmission anddelays the packet transmission when other packets are detected.

Here, in 802.11, a known signal sequence called a physical layerconvergence protocol (PLCP) preamble is used to detect a packettransmitted from another communication apparatus. Specifically,detection of a packet is performed by correlating a signal sequence of areceived packet with a known signal sequence.

However, information amounts of content to be transmitted and the numberof products supporting a wireless LAN are continuously increasing, andthus it is desirable to further improve communication throughput.

Here, the PLCP preamble is used for processes for reception of packets,for example, detection of a start timing of a packet, gain adjustment ofa communication apparatus at a reception side, channel estimation,correction of a frequency offset, and the like. However, when packetscan be received without performing the above processes, an unnecessaryPLCP preamble is transmitted, and the overhead of communicationincreases.

On the other hand, there is a technique of reducing the overhead ofcommunication by the PLCP preamble. For example, in Non-PatentLiterature 1, a green field format is defined as a PLCP format, and atraining signal for securing backward compatibility is not included inthe PLCP of the format. The overhead of communication is reducedaccordingly.

CITATION LIST Non-Patent Literature

-   Non-Patent Literature 1: 802.11 2012 IEEE Standard for Information    technology-Telecommunications and information exchange between    systems Local and metropolitan area networks-Specific requirements    Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer    (PHY) Specifications

DISCLOSURE OF INVENTION Technical Problem

However, even in the case of the green field format, since othertraining signals are included, there are cases in which an unnecessaryPLCP preamble is transmitted.

In this regard, the present disclosure proposes a communicationapparatus and a communication method, which are novel and improved andcapable of reducing the overhead of communication while suppressinginfluence on a frame reception process.

Solution to Problem

According to the present disclosure, there is provided a communicationapparatus, including: a processing unit configured to select one of aframe of a first format including a training signal and a frame of asecond format not including a first field which is at least a part ofthe training signal, and generate the frame of the selected format; anda communication unit configured to transmit the frame of the firstformat or the frame of the second format.

According to the present disclosure, there is provided a communicationapparatus, including: a communication unit configured to receive a frameof a first format including a training signal and a frame of a secondformat not including a first field which is at least a part of thetraining signal.

According to the present disclosure, there is provided a communicationmethod, including: selecting one of a frame of a first format includinga training signal and a frame of a second format not including a firstfield which is at least a part of the training signal, and generatingthe frame of the selected format; and transmitting the frame of thefirst format or the frame of the second format.

Advantageous Effects of Invention

As described above, according to the present disclosure, a communicationapparatus and a communication method which are capable of reducing theoverhead of communication while suppressing influence on a framereception process are provided. Note that the effects described aboveare not necessarily limitative. With or in the place of the aboveeffects, there may be achieved any one of the effects described in thisspecification or other effects that may be grasped from thisspecification.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an example configuration of acommunication system according to an embodiment of the presentdisclosure.

FIG. 2A is a diagram illustrating a frame format of a mixed modesupported by 802.11n/ac.

FIG. 2B is a diagram illustrating a frame format supported by 802.11a/g.

FIG. 3 is a diagram illustrating a frame exchange sequence according toa related art.

FIG. 4 is a block diagram illustrating a schematic functionalconfiguration of a communication apparatus according to a firstembodiment of the present disclosure.

FIG. 5 is a diagram illustrating an example configuration of a frameincluding information indicating a T_(VSP) candidate time lengthaccording to the present embodiment.

FIG. 6A is a diagram illustrating an example of a VSP frame in thepresent embodiment.

FIG. 6B is a diagram illustrating an example of a VSP frame having ashorter PLCP than the VSP frame illustrated in FIG. 6A according to thepresent embodiment.

FIG. 6C is a diagram illustrating an example of a VSP frame having ashorter PLCP than the VSP frame illustrated in FIG. 6B according to thepresent embodiment.

FIG. 7 is a flowchart conceptually illustrating a PLCP selection processof a communication apparatus according to the present embodiment.

FIG. 8 is a flowchart conceptually illustrating a reception methodselection process of a communication apparatus according to the presentembodiment.

FIG. 9 is a diagram illustrating a frame exchange sequence performed ina communication system according to the present embodiment.

FIG. 10 is a flowchart conceptually illustrating a PLCP selectionprocess of a communication apparatus according to a first modifiedexample of the present embodiment.

FIG. 11 is a diagram illustrating an example of a frame including a VSPframe use request according to a second embodiment of the presentdisclosure.

FIG. 12 is a flowchart conceptually illustrating a PLCP designationprocess and a PLCP selection process of a communication apparatusaccording to the present embodiment.

FIG. 13 is a flowchart conceptually illustrating a reception methodselection process of a communication apparatus according to the presentembodiment.

FIG. 14 is a diagram illustrating a frame exchange sequence fordescribing an example of a process of a communication system accordingto the present embodiment.

FIG. 15 is a diagram illustrating an example of a frame exchangesequence performed in one-to-many communication according to a relatedart.

FIG. 16 is a block diagram illustrating a schematic functionalconfiguration of a communication apparatus according to a thirdembodiment of the present disclosure.

FIG. 17 is a flowchart conceptually illustrating a PLCP selectionprocess of a communication apparatus according to the presentembodiment.

FIG. 18 is a diagram illustrating a frame exchange sequence fordescribing an example of a process of a communication system accordingto the present embodiment.

FIG. 19 is a diagram illustrating an example of a frame exchangesequence performed in communication according to a related art when aPLCP is added independently.

FIG. 20 is a diagram illustrating a frame exchange sequence fordescribing an example of a process of a communication system accordingto a fourth embodiment of the present disclosure.

FIG. 21 is a block diagram illustrating an example schematicconfiguration of a smartphone.

FIG. 22 is a block diagram illustrating an example schematicconfiguration of a car navigation device.

FIG. 23 is a block diagram illustrating an example schematicconfiguration of a wireless access point.

MODE(S) FOR CARRYING OUT THE INVENTION

Hereinafter, (a) preferred embodiment(s) of the present disclosure willbe described in detail with reference to the appended drawings. In thisspecification and the appended drawings, structural elements that havesubstantially the same function and structure are denoted with the samereference numerals, and repeated explanation of these structuralelements is omitted.

Further, description will proceed in the following order.

1. Overview of information system related to one embodiment of presentdisclosure

2. First embodiment (example in which PLCP is autonomously selected)

3. Second embodiment (example in which requested PLCP is selected)

4. Third embodiment (example in which PLCP is selected in space divisionmultiplexing communication)

5. fourth embodiment (example in which PLCP is selected in frequencydivision multiplexing communication)

6. Application examples

7. Conclusion

1. OVERVIEW OF INFORMATION SYSTEM ACCORDING TO EMBODIMENT OF PRESENTDISCLOSURE

Firstly, an overview of a communication system according to anembodiment of the present disclosure will be described with reference toFIG. 1. FIG. 1 is a diagram illustrating an example configuration of thecommunication system of the embodiment of the present disclosure.

The communication system is configured with a plurality of communicationapparatuses 10. The communication apparatuses 10 have a wirelesscommunication function and operate as access points (APs) or terminals.Hereinafter, a communication apparatus 10 operating as an AP will alsobe referred to as a master unit, and communication apparatuses 10operating as terminals will be referred to as slave units. For thisreason, in the communication system, communication is possible betweenthe master unit and the slave units. Here, communication from the masterunit to the slave units is referred to as downlink (DL) communication,and communication from the slave units to the master unit is referred toas uplink (UL) communication.

For example, as shown in FIG. 1, the communication system may include aplurality of communication apparatuses 10#0 to 10#4. The communicationapparatus 10#0 which is a master unit and the communication apparatuses10#1 to 10#4 which are slave units are connected through wirelesscommunication and directly transmit and receive frames to and from eachother.

Here, in the 802.11 standard, the PLCP preamble used for the framereception process is added to the frames to be transmitted/received. Aconfiguration of a frame according to a related art will be describedwith reference to FIGS. 2A and 2B. FIG. 2A is a diagram illustrating aformat of a frame supported by 802.11a/g (hereinafter, also referred toas a “legacy mode frame”), and FIG. 2B is a diagram illustrating a frameformat of a mixed mode supported by 802.11n/ac.

First, as illustrated in FIG. 2A, the legacy mode frame is configuredwith a legacy long training field (L-STF), a legacy short training field(L-LTF), a legacy signal field (L-SIG), a Service, and a physical layerservice data unit (PSDU).

Further, as illustrated in FIG. 2B, the mixed mode frame is configuredwith an L-STF, an L-LTF, an L-SIG, an Ext-SIG, an Ext-STF, an Ext-LTF, aService, and a PSDU. The Ext-STF or the like may be a high throughput(HT)-STF, a very high throughput (VHT)-STF, or the like.

As described above, the mixed mode has the PLCP preamble such as theL-STF in order to secure the backward compatibility with the legacymode. A PLCP used in frame exchange according to a related art will bedescribed with reference to FIG. 3. FIG. 3 is a diagram illustrating aframe exchange sequence according to a related art.

First, the master unit transmits a legacy mode transmission permissionrequest frame. For example, as illustrated in FIG. 3, the master unit10#0 transmits a request to send (RTS) frame to which the PLCP of thelegacy mode is added to slave units 10#1 and 10#2.

Then, the slave unit that has received the transmission permissionrequest frame transmits a legacy mode transmission permission frame tothe master unit. For example, as illustrated in FIG. 3, the slave unit10#1 transmits a clear to send (CTS) frame to which the PLCP of thelegacy mode is added to the master unit 10#0.

Then, the master unit that has received the transmission permissionframe transmits a mixed mode data frame to the slave unit. For example,as illustrated in FIG. 3, the master unit 10#0 transmits a data frame towhich the PLCP of the mixed mode is added to the slave unit 10#1.Thereafter, the PLCP of the mixed mode is added to each frame to betransmitted.

Since the PLCP preamble is added to the frame each time communication isperformed as described above, when a frame can be received withoutperforming the frame reception process using the PLCP preamble, anunnecessary PLCP preamble is transmitted. For this reason, the overheadof communication is likely to increase.

On the other hand, a frame of a green field format defined by 802.11n(hereinafter, also referred to as a “green field mode frame”) does notinclude a signal such as the L-STF in order to secure the backwardcompatibility with the legacy mode, unlike the mixed mode. However, evenin the case of the green field mode frame, since the PLCP preamble suchas the HT-STF is included, there is room for improvement incommunication efficiency.

In this regard, the present disclosure proposes a communicationapparatus and a communication method which are capable of reducing theoverhead of communication while suppressing influence on the framereception process. Details thereof will be described below. Here,although an example of a communication system in which the communicationapparatus 10#0 is a master unit is described in FIG. 1, anothercommunication apparatus 10 may be a master unit, or the communicationapparatus 10#0 may be a communication apparatus having a plurality ofdirect links with other communication apparatuses 10#1 to 10#4. In thelatter case, the aforementioned UL may be replaced with “simultaneoustransmission from one unit to a plurality of units,” and theaforementioned UL may be replaced with “simultaneous transmission from aplurality of units to one unit.” Also, for convenience of description,communication apparatuses 10 according to first to fourth embodimentsare distinguished by attaching numbers corresponding to the embodimentsto the ends thereof, such as a communication apparatus 10-1 and acommunication apparatus 10-2.

2. FIRST EMBODIMENT (EXAMPLE IN WHICH PLCP IS AUTONOMOUSLY SELECTED)

The overview of the communication system according to one embodiment ofthe present disclosure has been described above. Next, a communicationapparatus 10-1 according to a first embodiment of the present disclosurewill be described. The communication apparatus 10-1 according to thepresent embodiment autonomously selects the PLCP to be added to theframe to be transmitted. The selected PLCP is also called a PLCP of arelated art or a PLCP which is shorter than the PLCP of the related art(hereinafter, also referred to as a “very short PLCP (VSP)).

2-1. Configuration of Communication Apparatus

Firstly, a configuration of the communication apparatus 10-1 accordingto the first embodiment of the present disclosure will be described withreference to FIG. 4. FIG. 4 is a block diagram schematicallyillustrating a functional configuration of the communication apparatus10-1 of the first embodiment of the present disclosure.

As illustrated in FIG. 4, the communication apparatus 10-1 includes adata processing unit 11, a communication unit 12, and a control unit 15.Firstly, basic functions of the communication apparatus 10-1 will bedescribed.

((Basic Functions))

The data processing unit 11 performs a process for transmission andreception of data. Specifically, the data processing unit 11 generates aframe on the basis of data from a higher-level layer of communication,and provides the generated frame to a modulation/demodulation unit 13described below. For example, the data processing unit 11 generates aframe (or packets) from data, and performs processes, such as additionof a MAC header for media access control (MAC), addition of an errordetection code, and the like, on the generated frame. The dataprocessing unit 11 also extracts data from a received frame, andprovides the extracted data to a higher-level layer of communication.For example, the data processing unit 11 obtains data by performing, ona received frame, analysis of a MAC header, detection and correction ofcode error, a reordering process, and the like

As illustrated in FIG. 4, the communication unit 12 includes amodulation/demodulation unit 13 and radio interface units 14.

The modulation/demodulation unit 13 performs a modulation process andthe like on a frame. Specifically, the modulation/demodulation unit 13performs encoding, interleaving, and modulation on a frame provided bythe data processing unit 11, in accordance with coding and modulationschemes and the like set by the control unit 15, to generate a symbolstream. Thereafter, the modulation/demodulation unit 13 provides thegenerated symbol stream to the radio interface unit 14. Themodulation/demodulation unit 13 also performs demodulation and decodingor the like on the symbol stream provided by radio interface unit 14 toobtain a frame, and provides the obtained frame to the data processingunit 11 or the control unit 15.

The radio interface unit 14, which includes an antenna, transmits andreceives a signal through the antenna. Specifically, the radio interfaceunit 14 converts a signal contained in a symbol stream provided from themodulation/demodulation unit 13, into an analog signal, and performsamplification, filtering, and frequency upconversion on the analogsignal. Thereafter, the radio interface unit 14 transmits the processedsignal through the antenna. The radio interface unit 14 also performs,on a signal from the antenna, reverse processes to those which areperformed for signal transmission, such as frequency downconversion,digital signal conversion, and the like, and provides the signalobtained by the processes to the modulation/demodulation unit 13.

Further, two or more radio interface units 14 may be provided.Hereinafter, the modulation/demodulation unit 13 and the radio interfaceunit 14 are collectively referred to as a “communication unit 12.”

The control unit 15 controls an overall operation of the communicationapparatus 10-1. Specifically, the control unit 15 transfers informationbetween each function, sets communication parameters, and schedulesframes (or packets) in the data processing unit 11, for example.

(Parameter Decision Function)

The control unit 15 decides a parameter used in the PLCP selectionprocess. Specifically, the control unit 15 decides a time in which acommunication synchronization error with a communication linkdestination falls within a predetermined range. A communicationsynchronization target in the present disclosure will be describedlater.

More specifically, when a communication link is established, the controlunit 15 first determines whether the communication apparatus with whichthe communication link is established is the communication apparatus10-1 corresponding to the VSP. For example, at the time of association,the control unit 15 makes an attempt to acquire information indicatingthat it is a VSP-supporting communication apparatus using an associationrequest or response.

When the communication apparatus with which the communication link isestablished is determined not to be a communication apparatus supportingthe VSP, the control unit 15 turns off a VSP setting. For example, whenit is unable to acquire information indicating that the communicationapparatus of the communication link destination is the communicationapparatus supporting the VSP, the control unit turns off the VSP settingin communication with the communication apparatus, for example, sets itto disable or the like. When the information is acquired, the controlunit 15 may turn on the VSP setting in communication with thecommunication apparatus, for example, set it to enable or the like.

Then, the control unit 15 calculates an estimated time length until thecommunication synchronization error falls within a predetermined range(hereinafter, also referred to as a “T_(VSP) candidate time length”).Here, the communication synchronization error indicates, for example, atiming synchronization error with the communication apparatus 10-1 withwhich the communication link is established, a frequency synchronizationerror with the communication apparatus 10-1, and a channel estimationerror with the communication apparatus 10-1. Then, the control unit 15calculates a time length in which the timing synchronization error withthe communication apparatus 10-1 with which the communication link isestablished is determined to fall within a predetermined range, a timelength in which the frequency synchronization error with thecommunication apparatus 10-1 is determined to fall within apredetermined range, and a time length in which the channel estimationerror with the communication apparatus 10-1 is determined to fall withina predetermined range. The control unit 15 may calculate only a part ofthe time length as the T_(VSP) candidate time length.

Then, the control unit 15 shares the calculated T_(VSP) candidate timelength with the communication apparatus with which the communicationlink is established. For example, the control unit 15 generates a frameincluding information indicating each of the calculated T_(VSP)candidate time lengths (hereinafter, also referred to as a “T_(VSP)exchange frame”) to the data processing unit 11, and causes thecommunication unit 12 to transmit the T_(VSP) exchange frame to thecommunication apparatus. Further, the T_(VSP) exchange frame used forsharing of the T_(VSP) candidate time length will be described withreference to FIG. 5. FIG. 5 is a diagram illustrating an exampleconfiguration of the T_(VSP) exchange frame including the informationindicating the T_(VSP) candidate time length according to the presentembodiment.

As illustrated in FIG. 5, the T_(VSP) exchange frame is configured witha PLCP, a MAC header, a frame body, and a frame check sequence (FCS),and the information indicating the T_(VSP) candidate time length may bestored in the frame body. For example, the information indicating theT_(VSP) candidate time length may be configured with an Action Category,an Action ID (identification), and a My T_(VSP) Value. For example, acategory of information, for example, “VSP,” is stored in the ActionCategory, a type of information within the category, for example, “VSPCondition Notify,” is stored in the Action ID, and a value of theinformation, that is, the information indicating the T_(VSP) candidatetime length, is stored in the My T_(VSP) Value.

Returning to the description of the configuration of the communicationapparatus 10-1 according to the present embodiment with reference toFIG. 4, the control unit 15 then decides a time in which thecommunication synchronization error falls within a predetermined rangeon the basis of the time lengths received from the communicationapparatus with which the communication link is established and thecalculated time lengths. For example, the control unit 15 selects thetime length shorter than other time lengths among the time lengthsindicated by the information included in the received frame and thecalculated time lengths as a predetermined time T_(VSP) used in the PLCPselection process.

(PLCP Selection Function)

The control unit 15 selects the PLCP to be added to the frame to betransmitted as a part of the processing unit. Specifically, the controlunit 15 selects the PLCP so that a frame including the training signalis generated as a frame of a first format, or a frame not including atleast a part of the training signal is generated as a frame of a secondformat. For example, the control unit 15 selects either the PLCP of therelated art or the VSP.

More specifically, the control unit 15 selects the VSP when a conditionrelated to a transmission time of a frame serving as a first conditionis satisfied. For example, the control unit 15 selects the VSP when apredetermined time does not elapse after a frame to which the PLCP ofthe related art is added (hereinafter, also referred to as an “originalframe”) is transmitted, and a transmission time of the frame to betransmitted is known to the destination of the frame to be transmitted.The transmission time may have a temporal width.

The data processing unit 11 generates a frame on the basis of the PLCPselected by the control unit 15. Specifically, the data processing unit11 generates the original frame or the frame to which the VSP is added(hereinafter, also referred to as a “VSP frame”). Further, a VSP framegeneration process of the data processing unit 11 will be described withreference to FIGS. 6A and 6B. FIG. 6A is a diagram illustrating anexample of a VSP frame according to the present embodiment, and FIG. 6Bis a diagram illustrating an example of a VSP frame having a shorterPLCP than the VSP frame illustrated in FIG. 6A. Further, FIG. 6C is adiagram illustrating an example of a VSP frame having a shorter PLCPthan the VSP frame illustrated in FIG. 6B.

The data processing unit 11 generates a frame in which the trainingsignal for the backward compatibility is not included. For example, whenthe frame is transmitted to the destination of the legacy mode frameafter the legacy mode frame is transmitted, the data processing unit 11generates a VSP frame configured with a PLCP including an L-SIG, anExt-SIG, an Ext-STF, an Ext-LTF, and a Service without including theL-STF and the like (hereinafter, also referred to as “VSP1”) and a PSDU(hereinafter, also referred to as a “VSP1 frame”) as illustrated in FIG.6A.

Further, the data processing unit 11 generates a frame configured with asignal including information related to a data part of the frame and thedata part. For example, when the mixed mode frame or the VSP1 frame istransmitted, and then the frame is further transmitted to thetransmission destination of the frame, the data processing unit 11generates a VSP frame configured with a PLCP including an SIG and aService without including the entire training signal such as the L-STFor the Ext-STF (hereinafter, also referred to as “VSP2”) and a PSDU(hereinafter, also referred to as a “VSP2 frame”) as illustrated in FIG.6B.

Further, the data processing unit 11 generates a frame configured withonly the data part of the frame. For example, when the mixed mode frameor VSP1 frame is transmitted, and then the frame is further transmittedto the transmission destination of the frame, the data processing unit11 generates a VSP frame configured with a PLCP including only a Servicewithout including the entire training signal such as the L-STF or theExt-STF and an SIG (hereinafter, also referred to as “VSP3”) and a PSDU(hereinafter, also referred to as a “VSP3 frame”) as illustrated in FIG.6C.

(Reception Method Selection Function)

The communication unit 12 receives the frame serving as the frame of thefirst format including the training signal and the frame serving as theframe of the second format not including at least a part of the trainingsignal. Specifically, the communication unit 12 performs the process ofreceiving the original frame and the VSP frame. Further, when apredetermined time elapses after the original frame is received, thecommunication unit 12 receives only the original frame.

2-2. Process of Communication Apparatus

Next, a process of the communication apparatus 10-1 according to thepresent embodiment will be described with reference to FIGS. 7 to 9.

(PLCP Selection Process)

First, the PLCP selection process will be described with reference toFIG. 7. FIG. 7 is a flowchart conceptually illustrating the PLCPselection process of the communication apparatus 10-1 according to thepresent embodiment.

First, the communication apparatus 10-1 determines whether a receptiontime of the frame to be transmitted is known to the reception side (stepS102). Specifically, the control unit 15 determines whether or not animmediate response to the frame to be transmitted is requested fromanother communication apparatus 10-1. For example, the control unit 15determines whether or not an immediate response request is previouslyreceived from the destination of the frame to be transmitted or whetheror not an immediate response request is included in a frame serving as aresponse to the original frame from the transmission destination.

When the immediate response is requested, the control unit 15 causes thecommunication unit 12 to transmit the frame when a predetermined timeknown to the communication apparatus 10-1 elapses after the frame isreceived from the transmission destination. For example, thepredetermined time is an inter frame space (IFS) such as a short interframe space (SIFS). Therefore, the communication apparatus 10-1 which isthe destination of the frame to be transmitted can detect the receptiontime of the VSP frame more accurately and reduce a possibility of thereception of the VSP frame failing.

Further, in a process of this step, the control unit 15 may determinewhether or not transmission of the frame to be transmitted is permittedwhen a predetermined time elapses after reception of a frame receivedlater than other frames. In this case, it can be estimated that thereception time of the frame to be transmitted is known to thedestination even if the transmission source of the frame receivedimmediately before its own apparatus transmits the frame differs fromthe destination of the frame to be transmitted.

When the reception time of the frame to be transmitted is determined tobe known to the reception side, the communication apparatus 10-1determines whether or not a predetermined time T_(VSP) elapses after thetraining signal is transmitted to the destination of the frame to betransmitted (Step S104). Specifically, in the parameter decisionprocess, the control unit 15 determines whether or not the time T_(VSP)decided as the time in which the communication synchronization errorfalls within a predetermined range elapses.

When the predetermined time T_(VSP) is determined not to elapse afterthe training signal is transmitted to the destination of the frame to betransmitted, the communication apparatus 10-1 determines whether or notthere is a non-transmitted training signal (step S106). Specifically,the control unit 15 determines whether or not the mixed mode frame orthe VSP1 frame has been transmitted to the destination of the frame tobe transmitted in the previous frame transmission.

When it is determined that there is no non-transmitted training signal,the communication apparatus 10-1 adds the PLCP (VSP2) not including thetraining signal or the PLCP (VSP3) including only the Service to theframe to be transmitted (step S108). Specifically, the control unit 15selects VSP2 when it is determined that the mixed mode frame or the VSP1frame has been transmitted to the destination of the frame to betransmitted in the previous frame transmission. Then, the dataprocessing unit 11 generates a frame to which the VSP2 is added.

Further, when the condition for selecting the VSP2 is satisfied, and theinformation related to the data part of the frame to be transmitted isuniquely decided, the control unit 15 may select the VSP3. For example,when the information related to the data part of the frame to betransmitted is shared between its own apparatus and the destination ofthe frame to be transmitted in advance, the control unit 15 selects theVSP3. In this case, the data processing unit 11 generates a frame towhich the VSP3 is added.

When it is determined that there is a non-transmitted training signal,the communication apparatus 10-1 adds the PLCP (VSP1) including thenon-transmitted training signal to the frame to be transmitted (stepS110). More specifically, the control unit 15 selects VSP1 when it isdetermined that the legacy mode frame has been transmitted to thedestination of the frame to be transmitted in the previous frametransmission. Then, the data processing unit 11 generates a frame towhich the VSP1 is added.

When it is determined in step S102 that the reception time of the frameto be transmitted is not known to the reception side or when it isdetermined in step S104 that the predetermined time T_(VSP) elapsesafter the training signal is transmitted to the destination of the frameto be transmitted, the communication apparatus 10-1 adds the PLCP of therelated art to the frame to be transmitted (step S112). Specifically,the control unit 15 selects the legacy mode or the mixed mode, and thedata processing unit 11 generates the mixed mode frame.

(Reception Method Selection Process)

Next, a reception method selection process will be described withreference to FIG. 8. FIG. 8 is a flowchart conceptually illustrating thereception method selection process of the communication apparatus 10-1according to the present embodiment.

First, the communication apparatus 10-1 determines whether or not thepredetermined time T_(VSP) elapses after the frame is received from theVSP-supporting apparatus (step S202). Specifically, the control unit 15determines whether or not T_(VSP) elapses after the frame is receivedfrom the communication apparatus 10-1 related to communication in whichthe VSP setting is not disabled.

When the predetermined time T_(VSP) is determined to elapse after theframe is received from the VSP supporting apparatus, the communicationapparatus 10-1 is on standby only for the frame including the PLCP ofthe related art (step S204). Specifically, when T_(VSP) is determined toelapse after the frame is received from the communication apparatus 10-1related to the communication in which the VSP setting is not disabled,the control unit 15 causes a state of the communication unit 12 totransition to a state in which only the process of receiving the frameincluding the PLCP of the related art is performed. Further, when theVSP frame is received in the state in which only the process ofreceiving the frame including the PLCP of the related art is performed,the communication unit 12 does not perform the process of receiving theVSP frame because the frame format is different.

When the predetermined time T_(VSP) is determined not to elapse afterthe frame is received from the VSP supporting apparatus, thecommunication apparatus 10-1 is on standby for both the frame includingthe PLCP of the related art and the frame including the VSP (step S206).Specifically, when T_(VSP) is determined not to elapse after the frameis received from the communication apparatus 10-1 related to thecommunication in which the VSP setting is not disabled, the control unit15 causes the state of the communication unit 12 to transition to thestate in which the process of receiving the frame including the VSP isperformed. In the process of receiving the VSP frame, informationobtained from the received training signal, for example, a channelestimation value (including a gain set value) is used.

(Specific Example of Communication)

Next, a specific example of communication performed according to theprocess of FIGS. 7 and 8 will be described with reference to FIG. 9.FIG. 9 is a diagram illustrating an example of a frame exchange sequenceperformed in the communication system according to the presentembodiment.

First, a master unit 10-1#0 transmits the legacy mode transmissionpermission request frame to slave units 10-1#1 and 10-1#2. Then, theslave unit 10-1#1 that has received the frame transmits the legacy modetransmission permission frame to the master unit 10-1#0. The mixed modemay be selected instead of the legacy mode.

Then, the master unit 10-1#0 that has received the transmissionpermission frame transmits the data frame which is the VSP1 frame to theslave unit 10-1#1. Then, the slave unit 10-1#1 that has received theframe transmits an ACK frame which is the VSP1 frame to the master unit10-1#0.

Then, the master unit 10-1#0 transmits the mixed mode frame to the slaveunit 10-1#2. Then, the slave unit 10-1#2 that has received the frametransmits a mixed mode ACK frame to the master unit 10-1#0. Instead ofthe mixed mode frame, the legacy mode frame may be transmitted, but inthis example, the mixed mode frame is described as being transmitted.

Then, the master unit 10-1#0 transmits the data frame which is the VSP2frame to the slave unit 10-1#1. Then, the slave unit 10-1#1 that hasreceived the frame transmits an ACK frame which is the VSP2 frame to themaster unit 10-1#0. Here, the original frame and the VSP frametransmitted and received between the master unit 10-1#0 and the slaveunit 10-1#1 are also received by other communication apparatuses 10-1.Therefore, the slave unit 10-1#1 receives the ACK frame transmitted fromthe slave unit 10-1#2 to the master unit 10-1#0 and can detect thereception time of the data frame destined for the slave unit 10-1#1which is transmitted from the master unit 10-1#0.

Then, the master unit 10-1#0 transmits the data frame which is the VSP2frame to the slave unit 10-1#2. Then, the slave unit 10-1#2 that hasreceived the frame transmits an ACK frame which is the VSP2 frame to themaster unit 10-1#0.

As described above, according to the first embodiment of the presentdisclosure, the communication apparatus 10-1 selects any one of theframe of the first format including the training signal and the frame ofthe second format including no first field which is at least a part ofthe training signal, generates the frame of the selected format, andtransmits the frame of the first format or the frame of the secondformat. Further, the communication apparatus 10-1 receives the frame ofthe first format including the training signal or the frame of thesecond format including no first field which is at least a part of thetraining signal. For this reason, it is possible to reduce the overheadof communication while suppressing influence on the frame receptionprocess since the already transmitted training signal is not included inthe PLCP.

Further, at least a part of the training signals includes the trainingsignal for backward compatibility. For this reason, for example, whenthe mixed mode frame including the training signal for backwardcompatibility is used and the legacy mode frame is already transmitted,the PLCP is shortened, and the overhead of communication can be reduced.

Further, the frame of the second format is configured with the signalincluding information related to the data part of the frame and the datapart and does not include the training signal. Therefore, since thetraining signal is not included, the PLCP can be further shortened, andthe overhead of communication can be further reduced.

Further, the frame of the second format is configured with only the datapart of the frame and does not include the signal including theinformation related to the data part and the training signal. Therefore,the PLCP is further shortened, and thus it is possible to further reducethe overhead of communication.

Further, the communication apparatus 10-1 selects the frame of thesecond format when the first condition related to the transmission timeof the frame to be transmitted is satisfied. Therefore, when the abovecondition is set so that the reception success rate of the VSP frame isimproved, it is possible to suppress the reception failure of the VSPframe and improve the use efficiency of the wireless communicationresources.

Further, the first condition includes that the transmission time of theframe to be transmitted be before a predetermined time elapses after theframe of the first format is transmitted to the destination of the frameto be transmitted. For this reason, when the communication state changesover time and the use of the received training signal is undesirable,the VSP frame is not transmitted, and thus the decrease in the receptionsuccess rate of the VSP frame can be suppressed.

Further, it is included that the predetermined time be a time in whichthe communication synchronization error falls within a predeterminedrange. Therefore, when the VSP frame is transmitted within the time inwhich the communication success rate is maintained, it is possible tofurther suppress the decrease in the reception success rate of the VSPframe.

Further, it is included that the predetermined time be a time shorterthan the other time among times decided by the transmission destinationof the frame of the first format and its own apparatus. For this reason,when the transmission condition of the VSP frame is set so that thecommunication synchronization error falls within an allowable range inboth of the communication apparatuses, it is possible to furthersuppress the decrease in the reception success rate of the VSP frame.

Further, the first condition includes a condition that the transmissiontime of the frame to be transmitted be known to the destination of theframe to be transmitted. Therefore, the communication apparatus 10-1that receives the VSP frame can be on standby in the state in which theprocess of receiving the VSP frame is possible, and it is possible tosuppress the occurrence of the reception failure of the VSP frame.

Further, the first condition includes that the frame of the first formatand the frame of the second format also be received by othercommunication apparatuses other than the transmission destination of theframe of the first format. For this reason, the communication apparatus10-1 in the non-communication state can detect a timing at which theframe is transmitted to the communication apparatus 10-1 withoutseparately performing the communication of notifying of the transmissiontiming, and it is possible to improve the efficiency of communicationwhile suppressing the occurrence of the reception failure of the VSPframe.

Further, “being known” mentioned above includes that the transmission ofthe frame to be transmitted be permitted when a predetermined timeelapses after reception of a frame received later than other frames.Therefore, the communication apparatus 10-1 serving as the destinationof the frame to be transmitted can detect the reception time of the VSPframe more accurately and reduce the possibility of the receptionfailure of the VSP frame.

Further, “being known” mentioned above includes that the frame receivedfrom another communication apparatus indicate the immediate responserequest. Therefore, since the transmission time of the frame to beexchanged is more accurately detected, it is possible to furthersuppress the occurrence of the reception failure of the VSP frame.

Further, when a predetermined time elapses after the frame is received,the communication apparatus 10-1 receives only the frame of the firstformat. Therefore, in the state in which it is not desirable to use thereceived training signal, the process of receiving the VSP frame is notperformed, and thus a load related to the reception process is reduced,and the power consumption of the communication apparatus 10-1 can besuppressed. The communication apparatus 10-1 may be consistently onstandby for both the original frame and the VSP frame. In this case,since switching of the standby process is not performed, the process canbe simplified.

2-3. Modified Examples

The first embodiment of the present disclosure has been described above.Note that this embodiment is not limited to the above examples. Modifiedexamples of the first and second embodiments will now be described.

First Modified Example

As a first modified example of the present embodiment, the VSP frame maybe transmitted when the first condition related to the transmission timeof the frame is satisfied and the communication apparatus 10-1 otherthan the destination of the frame to be transmitted or its own apparatusis in the state in which the frame is not transmitted. Further, the VSPframe may be transmitted when the first condition related to thetransmission time of the frame is satisfied and the transmission periodlength of the frame to be transmitted is a threshold value or less. Aprocess of the communication apparatus 10-1 according to the presentmodified example will be described with reference to FIG. 10. FIG. 10 isa flowchart conceptually illustrating the PLCP selection process of thecommunication apparatus 10-1 according to the first modified example ofthe present embodiment. Further, description of processes that aresubstantially the same as the processes according to the firstembodiment is omitted.

First, the communication apparatus 10-1 determines whether or not thereception time of the frame to be transmitted is known to the receptionside (step S302).

When the reception time of the frame to be transmitted is determined tobe known to the reception side, the communication apparatus 10-1determines whether or not the transmission period length of the frame tobe transmitted is a threshold value or less (step S304). Specifically,the control unit 15 determines whether or not the transmission periodlength other than the PLCP part of the frame to be transmitted, that is,the transmission period length other than the PLCP preamble and the PLCPheader, is a threshold value or less. Further, the control unit 15 mayperform the determination using a data length, for example, a bytelength instead of the transmission period length.

When the transmission period length of the frame to be transmitted isdetermined to be a threshold value or less, the communication apparatus10-1 determines that it is a transmission suppression period indicatedby a signal for suppressing the frame transmission of the communicationapparatus 10-1 other than the destination of the frame to be transmittedand its own apparatus (step S306). Specifically, the control unit 15determines whether or not the transmission permission request frame andthe transmission permission frame to the transmission permission requestframe are exchanged before the transmission of the frame to betransmitted. For example, the control unit 15 transmits the RTS frame,and determines whether or not the CTS frame indicating that transmissionto its own apparatus is permitted is received as the response to the RTSframe. In this case, since a network allocation vector (NAV) is set incommunication apparatuses 10-1 that receive the CTS frame other than itsown apparatus, the frame transmission of other communication apparatuses10-1 is suppressed in a period in which the NAV is valid. Further, theNAV setting according to the embodiment of the present disclosure may beperformed by an exchange of a frame other than the RTS frame and the CTSframe. For example, the NAV may be set by a DATA frame (including aQuality of Service (QoS) DATA frame as well) and an ACK (including ablock ack frame as well) instead of the RTS frame or the CTS frame.

When the frame transmission of the communication apparatus 10-1 otherthan the destination of the frame to be transmitted and its ownapparatus is determined to be suppressed, the communication apparatus10-1 determines whether or not a predetermined time T_(VSP) elapsesafter the training signal is transmitted to the destination of the frameto be transmitted (step S308), and performs the process of adding thePLCP in accordance with a determination result (steps S312 and S314).

When it is determined in step S304 that the transmission period lengthof the frame to be transmitted is greater than the threshold value orwhen it is determined in step S306 that the frame transmission of thecommunication apparatus 10-1 other than the destination of the frame tobe transmitted and its own apparatus is not suppressed, thecommunication apparatus 10-1 adds the PLCP of the related art to theframe to be transmitted (step S316).

As described above, according to the first modified example of thepresent embodiment, the first condition includes that it be thetransmission suppression period indicated by the signal which isexchanged between the destination of the frame to be transmitted and itsown apparatus and used for suppressing the frame transmission ofcommunication apparatuses other than the destination of the frame to betransmitted and its own apparatus. Here, when the frame transmissionfrom other communication apparatuses 10-1 is permitted, a mismatchoccurs between the type of frame transmitted from the master unit andthe type of frame for which the slave unit is on standby, and thepossibility of the reception failure of the VSP frame increases.Therefore, when the frame transmission of other communicationapparatuses 10-1 is suppressed, it is possible to suppress the decreasein the reception success rate of the VSP frame.

Further, in the communication apparatus 10-1, the first conditionincludes that the transmission period length of the frame to betransmitted be a threshold value or less. Here, as the transmissionperiod length of the frame to be transmitted increases, that is, as theamount of data to be transmitted increases, the risk of frame receptionfailure, for example, influence of the increase in consumption ofwireless communication resources and the increase in the transmissionperiod which are caused by the occurrence of retransmission, increases.Therefore, when the frame transmission period length exceeds thethreshold value, the frame transmission of the VSP frame is notperformed, and thus the risk can be prevented.

Second Modified Example

As a second modified example of the present embodiment, thecommunication apparatus 10-1 may check whether or not the transmissiontime of the frame to be transmitted is known to communicationapparatuses 10-1 other than the communication apparatus 10-1 in thecommunication state. Specifically, the control unit 15 causes thecommunication unit 12 to transmit the transmission permission request toother communication apparatuses 10-1, and when the transmissionpermission is received in response to the transmission permissionrequest from other communication apparatuses 10-1, the transmission timeof the frame to be transmitted is determined to be known to the othercommunication apparatus 10-1.

For example, the control unit 15 causes the communication unit 12 totransmit the RTS frame to other communication apparatuses 10-1 beforethe PLCP selection process is performed. When the CTS frame is receivedas the response to the RTS frame, the control unit 15 determines thatthe transmission time of the frame to be transmitted is known to thetransmission destination of the CTS frame.

As described above, according to the second modified example of thepresent embodiment, the communication apparatus 10-1 transmits thetransmission permission request to other communication apparatuses, andthe first condition includes that the transmission permission bereceived from other communication apparatuses in response to thetransmission permission request. Therefore, it is possible to suppressthe situation in which the VSP frame is transmitted to othercommunication apparatuses 10-1, and the reception of the VSP frame failsin the state in which other communication apparatuses 10-1 are unable todetect the transmission timing of the VSP frame and are not on standbyfor the VSP frame.

3. SECOND EMBODIMENT (EXAMPLE IN WHICH REQUESTED PLCP IS SELECTED)

The communication apparatus 10-1 according to the first embodiment ofthe present disclosure has been described above. Next, a communicationapparatus 10-2 according to the second embodiment of the presentdisclosure will be described. The communication apparatus 10-2 accordingto the present embodiment selects the PLCP to be added to the frame tobe transmitted on the basis of a request from a communication partner.

<3-1. Configuration of Communication Apparatus>

The communication apparatus 10-2 has substantially the same functionalconfiguration as that of the first embodiment, except for a portion ofthe functions of the data processing unit 11, the communication unit 12,and the control unit 15. Note that substantially the same functions asthose of the first embodiment will not be described.

(PLCP Designation Function)

The control unit 15 designates the PLCP to be added to the frametransmitted from the communication destination to its own apparatus.Specifically, the control unit 15 makes a decision regarding a VSP frameuse request on the basis of a certain condition related to thetransmission time of the frame serving as a second condition.

For example, the control unit 15 makes a decision for requesting thetransmission of the VSP frame when the transmission time of the frameincluding information related to the use request is before apredetermined time elapses after the original frame is received, and thetransmission time of the frame to be received as the response to theframe including the information related to the use request is known toits own apparatus. Further, the control unit 15 decides the type of VSPframe, that is, VSP1, VSP2, or VSP3, when the decision related to thepresence or absence of the VSP frame use request is made.

The data processing unit 11 generates a frame including a VSP frame userequest. Specifically, the data processing unit 11 generates a frameincluding information indicating the presence or absence of the VSPframe use request and the type of VSP frame decided by the control unit15. The frame including the VSP frame use request will be described withreference to FIG. 11. FIG. 11 is a diagram illustrating an example ofthe frame including the VSP frame use request according to the presentembodiment.

The data processing unit 11 generates a frame including informationindicating the presence or absence of the use request and the type. Forexample, the information related to the use request includes a flagindicating the presence or absence of the use request and the type(hereinafter, also referred to as a “use request flag”), for example,VSP req illustrated in FIG. 11, and may be stored in a Service field ofthe frame. A storage location of the use request flag is not limitedthereto, and the use request flag may be stored in any other field, forexample, a SIGNAL field, a Reserve field of a MAC header, or any otherfield dedicated thereto. Further, the use request flag indicates thatthere is no use request when the value is 0, that the VSP1 frame isrequested when the value is 1, that the VSP2 frame is requested when thevalue is 2, and that the VSP3 frame is requested when the value is 3.

(PLCP Selection Function)

The control unit 15 selects the PLCP on the basis of the informationrelated to the use request included in the received frame. Specifically,the control unit 15 selects the VSP when the transmission time of theframe to be transmitted is known to the destination of the frame to betransmitted, and the transmission of the VSP frame is requested throughthe information related to the received use request. VSP1, VSP2 or VSP3is selected on the basis of the type of VSP indicated by the informationrelated to the use request.

(Reception Method Selection Function)

The communication unit 12 selects the process of receiving the frame tobe transmitted on the basis of the use request to respond to the userequest decided by the control unit 15. Specifically, the communicationunit 12 is on standby for a frame of a type indicated by the informationrelated to the use request included in the transmitted frame. Forexample, the communication unit 12 is on standby for the original framewhen the value of the use request flag is 0, on standby for the VSP1frame when the value is 1, on standby for the VSP2 frame when the valueis 2, and on standby for the VSP3 frame when the value is 3.

<3-2. Process of Communication Apparatus>

Next, a process of the communication apparatus 10-2 according to thepresent embodiment will be described with reference to FIGS. 12 to 14.

First, a PLCP designation process and a PLCP selection process will bedescribed with reference to FIG. 12. FIG. 12 is a flowchart conceptuallyillustrating the PLCP designation process and the PLCP selection processof the communication apparatus 10-2 according to the present embodiment.Further, description of processes that are substantially the same as theprocesses of the first embodiment will be omitted.

(PLCP Designation Process)

First, the communication apparatus 10-2 determines whether or not thereception time of the response frame to the frame to be transmitted isknown (step S402). Specifically, the control unit 15 determines whetheror not the immediate response request is transmitted to the transmissiondestination of the frame to be transmitted. When the immediate responseis a fixed setting common to the communication apparatuses 10-2, theprocess of this step may be omitted.

When the reception time of the response frame to the frame to betransmitted is determined to be known, the communication apparatus 10-2determines whether or not the transmission of apparatuses other than thedestination of the frame to be transmitted and its own apparatus issuppressed (step S404).

When the transmission of apparatuses other than the destination of theframe to be transmitted and its own apparatus is determined to besuppressed, the communication apparatus 10-2 determines whether or not apredetermined time T_(VSP) elapses after the training signal is receivedfrom the destination of the frame to be transmitted (Step S406).

When a predetermined time T_(VSP) is determined not to elapse after thetraining signal is received from the destination of the frame to betransmitted, the communication apparatus 10-2 designates the VSP as thePLCP used for the response frame (step S408). Specifically, the controlunit 15 determines the presence or absence of a non-transmitted trainingsignal, selects VSP1 when there is a non-transmitted training signal,and designates “1” as the value of the use request flag. If there is nonon-transmitted training signal, the control unit 15 selects VSP2 anddesignates “2” as the value of the use request flag.

When the condition for selecting VSP2 is satisfied and the informationrelated to the data part of the frame to be transmitted is uniquelydecided, the control unit 15 may select VSP3 and set “3” as the value ofthe use request flag.

When a predetermined time T_(VSP) is determined to elapse after thetraining signal is received from the destination of the frame to betransmitted, the communication apparatus 10-2 designates the PLCP of therelated art as the PLCP used for the response frame (step S410).Specifically, the control unit 15 selects the PLCP of the related artand designates “0” as the value of the use request flag.

(PLCP Selection Process)

Then, the communication apparatus 10-2 determines whether or not thereception time of the frame to be transmitted is known to the receptionside (step S412).

When the reception time of the frame to be transmitted is determined tobe known to the reception side, the communication apparatus 10-2determines whether or not the VSP is designated in the frame mostrecently received from the destination of the frame to be transmitted(step S414). Specifically, the control unit 15 acquires the use requestflag of the frame which is received later than any of other receivedframes before the process of this step, and determines whether or notthe value of the use request flag is 0.

When the VSP is determined to be designated in the frame most recentlyreceived from the destination of the frame to be transmitted, thecommunication apparatus 10-2 adds the VSP designated in the receivedframe to the frame (step S416). Specifically, when the value of the userequest flag is determined not to be 0, the control unit 15 selects theVSP corresponding to the value designated by the use request flag. Forexample, the control unit 15 selects VSP1 when the value of the userequest flag is 1, selects VSP2 when the value is 2, and selects VSP3when the value is 3. Then, the data processing unit 11 adds the VSPselected by the control unit 15 to the frame to be transmitted.

When the VSP is determined not to be designated in the frame mostrecently received from the destination of the frame to be transmitted,the communication apparatus 10-2 adds the PLCP of the related art to theframe to be transmitted (step S418). Specifically, when the value of theuse request flag is determined to be 0, the control unit 15 selects thePLCP of the related art. For example, when the value of the use requestflag is 0, the control unit 15 selects the PLCP of the legacy mode orthe mixed mode. Then, the data processing unit 11 adds the PLCP selectedby the control unit 15 to the frame to be transmitted.

(Reception Method Selection Process)

Next, the reception method selection process will be described withreference to FIG. 13. FIG. 13 is a flowchart conceptually illustratingthe reception method selection process of the communication apparatus10-2 according to the present embodiment.

First, the communication apparatus 10-2 determines whether or not theframe in which the VSP is designated as the PLCP used for the responseframe is transmitted (step S502). Specifically, the control unit 15determines whether or not the value of the use request flag included inthe transmitted frame is designated to be 0.

When the frame in which the VSP is designated as the PLCP used for theresponse frame is determined not to be transmitted, the communicationapparatus 10-2 is on standby for only the frame including the PLCP ofthe related art (step S504). Specifically, when it is determined thatthe value of the use request flag is designated to be 0, the controlunit 15 causes the state of the communication unit 12 to transition tothe state in which the process of receiving the frame including the PLCPof the related art is performed.

When the frame in which the VSP is designated as the PLCP used for theresponse frame is determined to be transmitted, the communicationapparatus 10-2 is on standby for only the frame including the VSPdesignated in the transmission frame (step S506). Specifically, when itis determined that the value of the use request flag is set to 1, thecontrol unit 15 causes the state of the communication unit 12 totransition to the state in which the process of receiving the frameincluding the VSP1 is performed. Further, when it is determined that thevalue of the use request flag is set to 2, the control unit 15 causesthe state of the communication unit 12 to transition to the state inwhich the process of receiving the frame including the VSP2 isperformed. Further, when it is determined that the value of the userequest flag is set to 3, the control unit 15 causes the state of thecommunication unit 12 to transition to the state in which the process ofreceiving the frame including the VSP3 is performed. In the process ofreceiving the VSP frame, the information obtained from the receivedtraining signal, for example, the channel estimation value (includingthe gain set value) or the like, is used.

(Specific Example of Communication)

Next, a specific example of communication performed according to theprocess of FIG. 12 and FIG. 13 will be described with reference to FIG.14. FIG. 14 is a diagram illustrating an example of a frame exchangesequence performed in the communication system according to the presentembodiment. Further, description of processes that are substantially thesame as the processes of the first embodiment will be omitted.

First, a master unit 10-2#0 transmits the legacy mode transmissionpermission request frame including the use request flag having the valueof 0 to slave units 10-2#1 and 10-2#2. Then, the slave unit 10-2#1 thathas received the frame transmits the legacy mode transmission permissionframe including the use request flag having the value of 1 to the masterunit 10-2#0.

Then, the master unit 10-2#0 that has received the transmissionpermission frame including the use request flag having the value of 1transmits the data frame which is the VSP1 frame including the userequest flag having the value of 1 to the slave unit 10-2#1. Then, theslave unit 10-2#1 that has received the frame transmits the ACK framewhich is the VSP1 frame including the use request flag having the valueof 2 to the master unit 10-2#0.

Then, the master unit 10-2#0 transmits the mixed mode frame includingthe use request flag having the value of 0 to the slave unit 10-2#2.Then, the slave unit 10-2#2 that has received the frame transmits themixed mode ACK frame including the use request flag having the value of2 to the master unit 10-2#0.

Then, the master unit 10-2#0 transmits the data frame which is the VSP2frame including the use request flag having the value of 2 to the slaveunit 10-2#1. Then, the slave unit 10-2#1 that has received the frametransmits the ACK frame which is the VSP2 frame including the userequest flag having the value of 2 to the master unit 10-2#0.

Then, the master unit 10-2#0 transmits the data frame which is the VSP2frame including the use request flag having the value of 2 to the slaveunit 10-2#2. Then, the slave unit 10-2#2 that has received the frametransmits the ACK frame which is the VSP2 frame including the userequest flag having the value of 2 to the master unit 10-2#0.

Thus, according to the second embodiment of the present disclosure, thecommunication apparatus 10-2 transmits the VSP frame when the frameincluding the VSP frame use request is received. Therefore, since thePLCP is selected on the basis of the use request of which the receptionside notifies, more appropriate PLCP is selected than when the PLCP isselected according to the determination of the transmitting side, and itis possible to suppress the occurrence of the frame reception failurecaused by erroneous selection of the PLCP.

Further, the communication apparatus 10-2 receives the frame includingthe use request for the frame of the second format which is transmittedwhen a second condition related to the transmission time of the frame issatisfied. Therefore, since the condition for the transmission of theuse request is set so that the reception success rate of the VSP frameis improved, it is possible to suppress the reception failure of the VSPframe and improve the use efficiency of the wireless communicationresources.

The second condition includes that the transmission time of the frameincluding the use request be before a predetermined time elapses afterthe frame of the first format is received from the destination of theframe including the use request, and that the transmission time of theframe received as the response to the frame including the use request beknown to the transmission source of the frame including the use request.Therefore, since the use request is transmitted in the situation inwhich the reception success rate of the VSP frame is higher than inother conditions, it is possible to suppress the occurrence of receptionfailure of the VSP frame.

Further, one of the frame of the first format and the frame of thesecond format is selected as a frame to be received, on the basis of theuse request included in the transmitted frame, and the frame of theselected format is received. Therefore, since only the frame of the PLCPformat requested by its own apparatus is awaited, it is possible toreduce the possibility of the frame reception failure and improve thecommunication efficiency.

In the above example, the presence or absence of the VSP frame userequest is indicated by the flag, but the presence or absence of the userequest may be indicated depending on whether or not the informationrelated to the use request is included in the frame.

4. THIRD EMBODIMENT (EXAMPLE IN WHICH PLCP IS SELECTED IN SPACE DIVISIONMULTIPLEXING COMMUNICATION)

The communication apparatus 10-2 related to the second embodiment of thepresent disclosure has been described above. Next, a communicationapparatus 10-3 according to the third embodiment of the presentdisclosure will be described. In the first and second embodiments,one-to-one communication between communication apparatuses is anapplication target, but in the present embodiment, one-to-manycommunication is an application target. First, one-to-many communicationaccording to a related art will be described with reference to FIG. 15.FIG. 15 is a diagram illustrating an example of a frame exchangesequence performed in one-to-many communication according to a relatedart.

First, the master unit transmits the legacy mode transmission permissionrequest frame. For example, as illustrated in FIG. 15, the master unit10#0 transmits the RTS frame to which the PLCP of the legacy mode isadded to the slave unit 10#1.

Then, the slave unit that has received the transmission permissionrequest frame transmits the legacy mode transmission permission frame tothe master unit. For example, as illustrated in FIG. 15, the slave unit10#1 transmits the CTS frame to which the PLCP of the legacy mode isadded to the master unit 10#0.

Then, the master unit that has received the transmission permissionframe generates a plurality of data frames, and transmits the dataframes to which the PLCP of the mixed mode common to the generated dataframes is added to the slave unit using multiplexing communication. Forexample, as illustrated in FIG. 15, the master unit 10#0 transmits aplurality of data frames DATA #01 to DATA #04 to which the PLCP of themixed mode is added to the slave units 10#1 to 10#4 using space divisionmultiplexing communication. Then, the PLCP of the mixed mode is added tothe frame to be exchanged later.

As described above, even in the case of one-to-many communication, thePLCP preamble is added to the frame each time communication isperformed, and there are cases in which an unnecessary PLCP preamble istransmitted. Furthermore, since a plurality of communication apparatusestransmit the frames, the reduction in efficiency of wirelesscommunication resources may be greater than in the case of one-to-onecommunication. Therefore, the communication apparatus 10-3 according tothe present embodiment is based on the communication apparatus accordingto the first embodiment, and uses a common VSP as the PLCP of the framesto be multiplexed.

<4-1. Configuration of Communication Apparatus>

First, a configuration of the communication apparatus 10-3 according tothe third embodiment of the present disclosure will be described withreference to FIG. 16. FIG. 16 is a block diagram illustrating aschematic functional configuration of the communication apparatus 10-3according to the third embodiment of the present disclosure. Further,description of components and functions which are substantially the sameas in the first embodiment will be omitted.

As illustrated in FIG. 16, the communication unit 12 includes a signalprocessing unit 16 in addition to the modulation/demodulation unit 13and the radio interface unit 14.

The signal processing unit 16 performs a process involved inspace-division multiplex communication. Specifically, the signalprocessing unit 16 performs a signal process involved in spaceseparation, on a symbol stream provided by the modulation/demodulationunit 13, and provides symbol streams obtained by the process to therespective radio interface units 14. The signal processing unit 16 alsoperforms a spatial process, such as a symbol stream separation processor the like, on symbol streams obtained from the radio interface units14, and provides a symbol stream obtained by the process to themodulation/demodulation unit 13.

The data processing unit 11 generates a plurality of frames and adds aPLCP common to the plurality of frames. Specifically, the dataprocessing unit 11 generates frames destined for a plurality ofcommunication apparatuses 10-3, and adds the PLCP selected by thecontrol unit 15 to the generated frames in common.

<4-2. Process of Communication Apparatus>

Next, a process of the communication apparatus 10-3 according to thepresent embodiment will be described. The process is substantially thesame as the process according to the first embodiment except for thePLCP selection process, and thus only the PLCP selection process will bedescribed with reference to FIG. 17. FIG. 17 is a flowchart conceptuallyillustrating the PLCP selection process of the communication apparatus10-3 according to the present embodiment. Further, description ofprocesses that are substantially the same as the processes of the firstembodiment will be omitted.

(PLCP Selection Process)

First, the communication apparatus 10-3 determines whether or not thereception time of the frame to be transmitted is known to the receptionside (step S602).

When the reception time of the frame to be transmitted is determined tobe known to the reception side, the communication apparatus 10-3determines whether or not the transmission of apparatuses other than thedestination of the frame to be transmitted and its own apparatus issuppressed (step S604).

When the transmission of apparatuses other than the destination of theframe to be transmitted and its own apparatus is determined to besuppressed, the communication apparatus 10-3 determines whether or not apredetermined time T_(VSP) elapses after the training signal istransmitted to any one of the destinations of the frame to betransmitted (step S606). Specifically, for each of the communicationapparatuses 10-3 that is the destination of the frame to be transmitted,the control unit 15 determines whether or not T_(VSP) elapses after thetraining signal is transmitted to each of the communication apparatuses10-3, that is, after the original frame is transmitted. T_(VSP) isdecided and managed for each communication link with the communicationapparatus 10-3.

When a predetermined time T_(VSP) is determined not to elapse after thetraining signal is transmitted to all the destinations of the frame tobe transmitted, it is determined whether or not there is anon-transmitted training signal (step S608). The control unit 15 doesnot select VSP unless a predetermined time T_(VSP) is determined not toelapse after the training signal is transmitted to all the destinationsof the frames to be transmitted.

If it is determined that there is no non-transmitted training signal,the communication apparatus 10-3 adds the PLCP not including thetraining signal to the frame to be transmitted (step S610).Specifically, the control unit 15 selects VSP2 when the mixed mode frameor the VSP1 frame is determined to be transmitted to the destination ofthe frame to be transmitted in the previous frame transmission. Then,the data processing unit 11 adds VSP2 to each of the generated framesdestined for a plurality of communication apparatuses 10-3.

If it is determined that there is a non-transmitted training signal, thecommunication apparatus 10-3 adds the PLCP including the non-transmittedtraining to the frame to be transmitted (step S612). Specifically, thecontrol unit 15 selects VSP1 when the legacy mode frame is determined tobe transmitted to the destination of the frame to be transmitted in theprevious frame transmission. Then, the data processing unit 11 adds VSP1to each of the generated frames destined for a plurality ofcommunication apparatuses 10-3.

When the determination results of step S602 and step S604 are false andthe determination result of step S606 is true, the communicationapparatus 10-3 adds the PLCP of the related art to the frame to betransmitted (step S614). Specifically, the control unit 15 selects thelegacy mode or the mixed mode, and the data processing unit 11 adds thePLCP of the mixed mode to each of the generated frames destined for aplurality of communication apparatuses 10-3.

(Specific Example of Communication)

Next, a specific example of communication performed according to theprocess of FIG. 17 and the like will be described with reference to FIG.18. FIG. 18 is a diagram illustrating an example of frame exchangesequence performed in the communication system according to the presentembodiment. Further, description of processes that are substantially thesame as the processing of the first embodiment will be omitted.

First, a master unit 10-3#0 transmits the legacy mode transmissionpermission request frame to a slave unit 10-3#1. Then, the slave unit10-3#1 that has received the frame transmits the legacy modetransmission permission frame to the master unit 10-3#0.

Then, the master unit 10-3#0 that has received the transmissionpermission frame generates the data frame destined for the slave units10-3#1 to 10-3#4, and transmits the frames to which the PLCP of themixed mode common to the data frames is added to the slave units 10-3#1to 10-3#4 using space division multiplexing communication. Each of theslave units 10-3#1 to 10-3#4 that have received the frame transmits theACK frame that is the VSP1 frame to the master unit 10-3#0. Since theACK frames are consequently multiplexed, the master unit 10-3#0 receivesthe ACK frame by performing a process of separating the multiplexed ACKframe.

Then, the master unit 10-3#0 generates the data frames destined for theslave units 10-3#1 to 10-3#4, and transmits the frames to which the VSP2common to the data frames is added to the slave units 10-3#1 to 10-3#4using space division multiplexing communication. Each of the slave units10-3#1 to 10-3#4 that have received the frame transmits the ACK frame towhich VSP2 is added to the master unit 10-3#0.

As described above, according to the third embodiment of the presentdisclosure, the communication apparatus 10-3 generates a plurality ofVSP frames and transmits the plurality of VSP frames using spacedivision multiplexing communication. Therefore, since the PLCP preambleis reduced to be smaller than in one-to-many communication, it ispossible to reduce the overhead of communication and improve the useefficiency of the wireless communication resources.

<5. FOURTH EMBODIMENT (EXAMPLE IN WHICH PLCP IS SELECTED IN FREQUENCYDIVISION MULTIPLEXING COMMUNICATION)>

The communication apparatus 10-3 according to the third embodiment ofthe present disclosure has been described above. Next, a communicationapparatus 10-4 according to the fourth embodiment of the presentdisclosure will be described. In the fourth embodiment, the PLCP isadded to the frames to be multiplexed in common, but in the presentembodiment, the PLCP is independently added to each of the frames to bemultiplexed. First, communication according to a related art when thePLCP is added independently will be described with reference to FIG. 19.FIG. 19 is a diagram illustrating an example of a frame exchangesequence performed by communication according to a related art when PLCPis added independently.

First, the master unit transmits the legacy mode transmission permissionrequest frame. For example, as illustrated in FIG. 15, the master unit10#0 transmits the RTS frame to which the PLCP of the legacy mode isadded to the slave unit 10#1.

Then, the slave unit that has received the transmission permissionrequest frame transmits the legacy mode transmission permission frame tothe master unit. For example, as illustrated in FIG. 15, the slave unit10#1 transmits the CTS frame to which the PLCP of legacy mode is addedto the master unit 10#0.

Then, the master unit that has received the transmission permissionframe generates a plurality of data frames and adds the PLCP of themixed mode to each of the generated data frames independently. Then, themaster unit transmits each of the data frames to which the PLCP is addedto the slave unit using multiplexing communication. For example, asillustrated in FIG. 15, the master unit 10#0 transmits a plurality ofdata frames DATA #01 to DATA #04 to which the PLCP of the mixed mode isadded to the slave units 10#1 to #10#4 using frequency divisionmultiplexing communication. Then, the PLCP of the mixed mode is added toeach of frames to be exchanged later.

As described above, since the PLCP preamble is added to the frame eachtime communication is performed, there are cases in which an unnecessaryPLCP preamble is transmitted. In this regard, the communicationapparatus 10-4 according to the present embodiment is based on thecommunication apparatus according to the first embodiment, and uses anindividual VSP as the PLCP of each of the frames to be multiplexed.

<5-1. Configuration of Communication Apparatus>

The communication apparatus 10-4 have substantially the same functionalconfiguration as that of the first embodiment, except for a portion ofthe functions of the data processing unit 11 and the communication unit12. Note that substantially the same functions as those of the first tothird embodiments will not be described.

The modulation/demodulation unit 13 and the signal processing unit 16 inthe communication unit 12 perform a process involved infrequency-division multiplexing. Specifically, themodulation/demodulation unit 13 divides a frame provided from the dataprocessing unit 11 into portions, the number of which is equal to thenumber of subcarriers, and modulates each portion of the frame obtainedby the division. Thereafter, the modulation/demodulation unit 13combines signals obtained by the modulation, and provides the signalobtained by the combination to the signal processing unit 16. The signalprocessing unit 16 performs a process, such as addition of a guardinterval, or the like, on the signal provided from themodulation/demodulation unit 13, and provides a signal obtained by theprocess, i.e., a symbol stream, to the radio interface unit 14.

The signal processing unit 16 performs a process, such as removal of aguard interval, or the like, on the symbol stream related to receivedwaves provided from the radio interface unit 14, and provides a signalobtained by the process to the modulation/demodulation unit 13. Themodulation/demodulation unit 13 extracts a subcarrier signal from thesignal provided from the signal processing unit 16, and demodulates eachsubcarrier. Thereafter, the modulation/demodulation unit 13 combinesframes obtained by the demodulation, and provides the combined frame tothe data processing unit 11.

The data processing unit 11 generates a plurality of frames and adds thePLCP to each of the plurality of frames. Specifically, the dataprocessing unit 11 generates frames destined for a plurality ofcommunication apparatuses 10-3, and adds the PLCPs selected by thecontrol unit 15 to the generated frames.

<5-2. Process of Communication Apparatus>

Next, a specific example of communication performed in the communicationsystem according to the present embodiment will be described withreference to FIG. 20. FIG. 20 is a diagram illustrating an example of aframe exchange sequence performed in the communication system accordingto the present embodiment. Since the flow of a process of thecommunication apparatus 10-4 is substantially the same as the flow ofthe process according to the first embodiment, description thereof isomitted. Further, descriptions of processes that are substantially thesame as the processes of the first and third embodiments will beomitted.

(Specific Example of Communication)

First, a master unit 10-4#0 transmits the legacy mode transmissionpermission request frame to a slave unit 10-4#1. Then, the slave unit10-4#1 that has received the frame transmits the legacy modetransmission permission frame to the master unit 10-4#0.

Then, the master unit 10-4#0 that has received the transmissionpermission frame generates the data frames destined for the slave units10-4#1 to 10-4#4, and adds the PLCP of the mixed mode to each of thedata frames. Then, the master unit 10-4#0 transmits the frames to theslave units 10-4#1 to 10-4#4 using frequency division multiplexingcommunication. Then, each of the slave units 10-4#1 to 10-4#4 that havereceived the frame transmits the ACK frame which is the VSP1 frame tothe master unit 10-4#0.

Then, the master unit 10-4#0 generates the data frames destined for theslave units 10-4#1 to 10-4#4, and transmits the frames to which VSP2common to the data frames is divided to the slave units 10-4#1 to 10-4#4using frequency division multiplexing communication. Then, each of theslave units 10-4#1 to 10-4#4 that have received the frame transmits theACK frame to which VSP2 is added to the master unit 10-4#0.

As described above, according to the fourth embodiment of the presentdisclosure, the communication apparatus 10-3 generates a plurality ofVSP frames and transmits the plurality of VSP frames using frequencydivision multiplexing communication. Therefore, since the PLCP preambleis reduced, it is possible to reduce the overhead of communication andimprove the use efficiency of wireless communication resources.

Further, the communication apparatus 10-4 adds the PLCP to each of theframes to be multiplexed. Thus, since different PLCPs can be added tothe frames destined for the communication apparatuses 10-3 that differin the result of the PLCP selection process, when some frames do notsatisfy a VSP addition condition, the case in which the PLCP of therelated art is added to all the frames is reduced. Further, it ispossible to further promote the reduction in the overhead ofcommunication.

6. APPLICATION EXAMPLE

The technology according to the embodiments of the disclosure can beapplied to various products. For example, a slave unit among thecommunication apparatus 10 may be realized as mobile terminals such assmartphones, tablet PCs (Personal Computers), notebook PCs, portablegame terminals, or digital cameras, fixed-type terminals such astelevision receivers, printers, digital scanners, or network storages,or car-mounted terminals such as car navigation devices. In addition,the slave unit may be realized as terminals that perform M2M (Machine toMachine) communication (also referred to as MTC (Machine TypeCommunication) terminals) such as smart meters, vending machines,remotely controlled surveillance devices, or POS (Point Of Sale)terminals. Furthermore, the slave unit may be wireless communicationmodules mounted in such terminals (for example, integrated circuitmodules configured by one die).

On the other hand, for example, a master unit among the communicationapparatus 10 may be realized as a wireless LAN access point (alsoreferred to as a wireless base station) which has a router function ordoes not have a router function. The master unit may be realized as amobile wireless LAN router. The master unit may also be a wirelesscommunication module (for example, an integrated circuit moduleconfigured with one die) mounted on the device.

6-1. First Application Example

FIG. 21 is a block diagram showing an example of a schematicconfiguration of a smartphone 900 to which the technology of the presentdisclosure can be applied. The smartphone 900 includes a processor 901,a memory 902, a storage 903, an externally connected interface 904, acamera 906, a sensor 907, a microphone 908, a input device 909, adisplay device 910, a speaker 911, a wireless communication interface913, an antenna switch 914, an antenna 915, a bus 917, a battery 918,and an auxiliary controller 919.

The processor 901 may be, for example, a CPU (Central Processing Unit)or an SoC (System on Chip), and controls functions of an applicationlayer and other layers of the smartphone 900. The memory 902 includes aRAM (Random Access Memory) and a ROM (Read Only Memory), and storesprograms executed by the processor 901 and data. The storage 903 caninclude a storage medium such as a semiconductor memory or a hard disk.The externally connected interface 904 is an interface for connecting anexternally attached device such as a memory card or a USB (UniversalSerial Bus) device to the smartphone 900.

The camera 906 has an image sensor, for example, a CCD (Charge CoupledDevice) or a CMOS (Complementary Metal Oxide Semiconductor), to generatecaptured images. The sensor 907 can include a sensor group including,for example, a positioning sensor, a gyro sensor, a geomagnetic sensor,an acceleration sensor, and the like. The microphone 908 converts soundsinput to the smartphone 900 into audio signals. The input device 909includes, for example, a touch sensor that detects touches on a screenof the display device 910, a key pad, a keyboard, buttons, switches, andthe like, to receive manipulations or information inputs from a user.The display device 910 has a screen such as a liquid crystal display(LCD), or an organic light emitting diode (OLED) display to displayoutput images of the smartphone 900. The speaker 911 converts audiosignals output from the smartphone 900 into sounds.

The wireless communication interface 913 supports one or more wirelessLAN standards of IEEE 802.11a, 11b, 11g, 11n, 11ac, and 11ad, to executethe wireless LAN communication. The wireless communication interface 913can communicate with another device via a wireless LAN access point inan infrastructure mode. In addition, the wireless communicationinterface 913 can directly communicate with another device in a directcommunication mode such as an ad hoc mode or Wi-Fi Direct (registeredtrademark). Wi-Fi Direct is different from the ad hoc mode, and thus oneof two terminals operates as an access point. However, communication isperformed directly between the terminals. The wireless communicationinterface 913 can typically include a baseband processor, an RF (RadioFrequency) circuit, a power amplifier, and the like. The wirelesscommunication interface 913 may be a single-chip module on which amemory that stores a communication control program, a processor thatexecutes the program, and a relevant circuit are integrated. Thewireless communication interface 913 may support another kind ofwireless communication scheme such as a cellular communication scheme, ashort-range wireless communication scheme, or a proximity wirelesscommunication scheme in addition to the wireless LAN scheme. The antennaswitch 914 switches a connection destination of the antenna 915 for aplurality of circuits (for example, circuits for different wirelesscommunication schemes) included in the wireless communication interface913. The antenna 915 has a single or a plurality of antenna elements(for example, a plurality of antenna elements constituting a MIMOantenna), and is used for transmission and reception of wireless signalsfrom the wireless communication interface 913.

Note that the smartphone 900 may include a plurality of antennas (forexample, antennas for a wireless LAN or antennas for a proximitywireless communication scheme, or the like), without being limited tothe example of FIG. 21. In this case, the antenna switch 914 may beomitted from the configuration of the smartphone 900.

The bus 917 connects the processor 901, the memory 902, the storage 903,the externally connected interface 904, the camera 906, the sensor 907,the microphone 908, the input device 909, the display device 910, thespeaker 911, the wireless communication interface 913, and the auxiliarycontroller 919 to one another. The battery 918 supplies electric powerto each of the blocks of the smartphone 900 shown in FIG. 21 via powersupply lines partially indicated by dashed lines in the drawing. Theauxiliary controller 919 causes, for example, necessary minimumfunctions of the smartphone 900 to be operated in a sleep mode.

In the smartphone 900 shown in FIG. 21, the data processing unit 11, thecommunication unit 12, and the control unit 15 described with referenceto FIG. 4 may be mounted in the wireless communication interface 913. Atleast some of the functions may be mounted on the processor 901 or theauxiliary controller 919. For example, the control unit 15 causes theframe not including the transmitted training signal to be transmitted tothe communication unit 12, and thus it is possible to reduce theoverhead of communication.

Note that the smartphone 900 may operate as a wireless access point(software AP) as the processor 901 executes the function of an accesspoint at an application level. In addition, the wireless communicationinterface 913 may have the function of a wireless access point.

6-2. Second Application Example

FIG. 22 is a block diagram showing an example of a schematicconfiguration of a car navigation device 920 to which the technology ofthe present disclosure can be applied. The car navigation device 920includes a processor 921, a memory 922, a GPS (Global PositioningSystem) module 924, a sensor 925, a data interface 926, a content player927, a storage medium interface 928, an input device 929, a displaydevice 930, a speaker 931, a wireless communication interface 933, anantenna switch 934, an antenna 935, and a battery 938.

The processor 921 may be, for example, a CPU or an SoC controlling anavigation function and other functions of the car navigation device920. The memory 922 includes a RAM and a ROM storing programs executedby the processor 921 and data.

The GPS module 924 measures a position of the car navigation device 920(for example, latitude, longitude, and altitude) using GPS signalsreceived from a GPS satellite. The sensor 925 can include a sensor groupincluding, for example, a gyro sensor, a geomagnetic sensor, a pneumaticsensor, and the like. The data interface 926 is connected to anin-vehicle network 941 via, for example, a terminal that is notillustrated to acquire data generated on the vehicle side such as carspeed data.

The content player 927 reproduces content stored in a storage medium(for example, a CD or a DVD) inserted into the storage medium interface928. The input device 929 includes, for example, a touch sensor thatdetects touches on a screen of the display device 930, buttons,switches, and the like to receive manipulations or information inputsfrom a user. The display device 930 has a screen such as an LCD or anOLED display to display images of the navigation function or reproducedcontent. The speaker 931 outputs sounds of the navigation function orreproduced content.

The wireless communication interface 933 supports one or more wirelessLAN standards of IEEE 802.11a, 11b, 11g, 11n, 11ac, and 11ad, to executewireless LAN communication. The wireless communication interface 933 cancommunicate with another device via a wireless LAN access point in theinfrastructure mode. In addition, the wireless communication interface933 can directly communicate with another device in a directcommunication mode such as an ad hoc mode or Wi-Fi Direct. The wirelesscommunication interface 933 can typically have a baseband processor, anRF circuit, a power amplifier, and the like. The wireless communicationinterface 933 may be a single-chip module on which a memory that storesa communication control program, a processor that executes the program,and a relevant circuit are integrated. The wireless communicationinterface 933 may support another kind of wireless communication schemesuch as a short-range wireless communication scheme, a proximitywireless communication scheme, or the cellular communication scheme inaddition to the wireless LAN scheme. The antenna switch 934 switches aconnection destination of the antenna 935 for a plurality of circuitsincluded in the wireless communication interface 933. The antenna 935has a single or a plurality of antenna elements and is used fortransmission and reception of wireless signals from the wirelesscommunication interface 933.

Note that the car navigation device 920 may include a plurality ofantennas, without being limited to the example of FIG. 22. In this case,the antenna switch 934 may be omitted from the configuration of the carnavigation device 920.

The battery 938 supplies electric power to each of the blocks of the carnavigation device 920 shown in FIG. 22 via power supply lines partiallyindicated by dashed lines in the drawing. In addition, the battery 938accumulates electric power supplied from the vehicle.

In the car navigation device 920 shown in FIG. 22, the data processingunit 11, the communication unit 12, and the control unit 15 describedwith reference to FIG. 4 may be mounted in the wireless communicationinterface 933. At least some of the functions may be mounted on theprocessor 921. For example, the control unit 15 causes the frame notincluding the transmitted training signal to be transmitted to thecommunication unit 12, and thus it is possible to reduce the overhead ofcommunication.

Further, the wireless communication interface 933 may operate as themaster unit described above and may provide a wireless connection to aterminal of a user riding in a vehicle. At that time, for example, theoverhead of communication in the wireless connection is reduced, and thecommunication time is reduced, and thus it is possible to suppress thepower consumption of the terminal of the user.

The technology of the present disclosure may be realized as anin-vehicle system (or a vehicle) 940 including one or more blocks of theabove-described car navigation device 920, an in-vehicle network 941,and a vehicle-side module 942. The vehicle-side module 942 generatesvehicle-side data such as a vehicle speed, the number of enginerotations, or failure information and outputs the generated data to thein-vehicle network 941.

6-3. Third Application Example

FIG. 23 is a block diagram showing an example of a schematicconfiguration of a wireless access point 950 to which the technology ofthe present disclosure can be applied. The wireless access point 950includes a controller 951, a memory 952, an input device 954, a displaydevice 955, a network interface 957, a wireless communication interface963, an antenna switch 964, and an antenna 965.

The controller 951 may be, for example, a CPU or a digital signalprocessor (DSP) and operates various functions (for example, accesslimitation, routing, encryption, a fire wall, and log management) of theInternet Protocol (IP) layer and higher layers of the wireless accesspoint 950. The memory 952 includes a RAM and a ROM and stores a programexecuted by the controller 951 and various kinds of control data (forexample, a terminal list, a routing table, an encryption key, securitysettings, and a log).

The input device 954 includes, for example, a button or a switch, andreceives a manipulation from a user. The display device 955 includes anLED lamp and displays an operation status of the wireless access point950.

The network interface 957 is a wired communication interface thatconnects the wireless access point 950 to a wired communication network958. The network interface 957 may include a plurality of connectionterminals. The wired communication network 958 may be a LAN such asEthernet (registered trademark) or may be a Wide Area Network (WAN).

The wireless communication interface 963 supports one or more wirelessLAN standards of IEEE 802.11a, 11b, 11g, 11n, 11ac, and 11ad, to supplywireless connection to a nearby terminal as an access point. Thewireless communication interface 963 can typically include a basebandprocessor, an RF circuit, and a power amplifier. The wirelesscommunication interface 963 may be a one-chip module in which a memorystoring a communication control program, a processor executing theprogram, and relevant circuits are integrated. The antenna switch 964switches a connection destination of the antenna 965 among a pluralityof circuits included in the wireless communication interface 963. Theantenna 965 includes one antenna element or a plurality of antennaelements and is used to transmit and receive a wireless signal throughthe wireless communication interface 963.

In the wireless access point 950 shown in FIG. 23, the data processingunit 11, the communication unit 12, and the control unit 15 describedwith reference to FIG. 4 may be mounted on the wireless communicationinterface 963. At least some of the functions may be mounted on thecontroller 951. For example, the control unit 15 causes the frame notincluding the transmitted training signal to be transmitted to thecommunication unit 12, and thus it is possible to reduce the overhead ofcommunication.

7. CONCLUSION

According to the first embodiment of the present disclosure, the alreadytransmitted training signal is not included in the PLCP, and thus it ispossible to reduce the overhead of communication while suppressinginfluence on the frame reception process.

According to the second embodiment of the present disclosure, the PLCPis selected on the basis of the use request of which the reception sidenotifies, and thus more appropriate PLCP is selected than when the PLCPis selected through the determination of the transmission side, and itis possible to suppress the occurrence of the frame reception failurewhich is caused by the erroneous selection of the PLCP.

Further, according to the third embodiment of the present disclosure,the PLCP preamble is reduced even in one-to-many communication, and thusit is possible to reduce the overhead of communication and improve theuse efficiency of the wireless communication resources.

Further, according to the fourth embodiment of the present disclosure,the PLCP preamble is reduced, and thus it is possible to reduce theoverhead of communication and improve the use efficiency of wirelesscommunication resources.

The preferred embodiment(s) of the present disclosure has/have beendescribed above with reference to the accompanying drawings, whilst thepresent disclosure is not limited to the above examples. A personskilled in the art may find various alterations and modifications withinthe scope of the appended claims, and it should be understood that theywill naturally come under the technical scope of the present disclosure.

For example, in the first and second embodiments, the example in whichthe frame is transmitted from the master unit to the slave unit has beendescribed, but the present technology is not limited to this example.For example, using the Reverse Direction function, a frame may betransmitted to the master unit continuously from the slave unit that hasreceived the frame from the master unit.

In the above embodiments, VSP1, VSP2, and VSP3 have been described asthe examples of the PLCP (VSP) in which a part or all of the trainingsignal is omitted, but the VSP is not limited thereto, and various PLCPsin which the training signal is omitted so that the frame receptionprocess can be performed may be employed as the VSP.

Further, not only a process in which steps shown in the flowcharts ofthe above embodiments are performed in a time-series manner inaccordance with a described sequence but also a process in which thesteps are not necessarily processed in a time-series manner but areexecuted in parallel or individually is included. Also, it isself-evident that even steps processed in a time-series manner can beappropriately changed in sequence depending on circumstances.

Further, the effects described in this specification are merelyillustrative or exemplified effects, and are not limitative. That is,with or in the place of the above effects, the technology according tothe present disclosure may achieve other effects that are clear to thoseskilled in the art from the description of this specification.

Additionally, the present technology may also be configured as below.

(1)

A communication apparatus, including:

a processing unit configured to select one of a frame of a first formatincluding a training signal and a frame of a second format not includinga first field which is at least a part of the training signal, andgenerate the frame of the selected format; and

a communication unit configured to transmit the frame of the firstformat or the frame of the second format.

(2)

The communication apparatus according to (1),

wherein the first field includes a training signal for backwardcompatibility.

(3)

The communication apparatus according to (1),

wherein the frame of the second format is configured with a signalincluding information related to a data part of a frame and the datapart, and does not include the training signal.

(4)

The communication apparatus according to (1),

wherein the frame of the second format is configured with only a datapart of a frame, and does not include a signal including informationrelated to the data part and the training signal.

(5)

The communication apparatus according to any one of (1) to (3),

wherein the processing unit selects the frame of the second format whena first condition related to a transmission time of a frame to betransmitted is satisfied.

(6)

The communication apparatus according to (5),

wherein the first condition includes that the transmission time of theframe to be transmitted be before a predetermined time elapses after theframe of the first format is transmitted to a destination of the frameto be transmitted.

(7)

The communication apparatus according to (6),

wherein the predetermined time is a time in which a communicationsynchronization error falls within a predetermined range.

(8)

The communication apparatus according to (6),

wherein the predetermined time is a time shorter than the other timeamong times decided by the transmission destination of the frame of thefirst format and the communication apparatus.

(9)

The communication apparatus according to any one of (5) to (8),

wherein the first condition includes that the transmission time of theframe to be transmitted be known to the destination of the frame to betransmitted.

(10)

The communication apparatus according to (9),

wherein being known includes that transmission of the frame to betransmitted be permitted when a predetermined time elapses afterreception of a frame received later than other frames.

(11)

The communication apparatus according to (9),

wherein being known includes that a frame received from anothercommunication apparatus indicates an immediate response request.

(12)

The communication apparatus according to any one of (5) to (11),

wherein the first condition includes that it be a transmissionsuppression period indicated by a signal which is exchanged between thedestination of the frame to be transmitted and the communicationapparatus and used for suppressing transmission of communicationapparatuses other than the destination of the frame to be transmittedand the communication apparatus.

(13)

The communication apparatus according to any one of (5) to (12),

wherein the first condition includes that a transmission period lengthof the frame to be transmitted be a threshold value or less.

(14)

The communication apparatus according to any one of (5) to (13),

wherein, when frames to be transmitted to a plurality of destinationsare multiplexed, the processing unit selects the frame of the secondformat when the first condition is satisfied for all the plurality ofdestinations.

(15)

The communication apparatus according to any one of (1) to (4),

wherein the processing unit selects the frame of the second format whena frame including a use request for the frame of the second format isreceived.

(16)

The communication apparatus according to (15),

wherein the communication unit receives the frame including the userequest for the frame of the second format which is transmitted when asecond condition related to a transmission time of a frame is satisfied.

(17)

The communication apparatus according to (16),

wherein the second condition includes that a transmission time of theframe including the use request be before a predetermined time elapsesafter the frame of the first format is received from a destination ofthe frame including the use request, and that a transmission time of aframe received as a response to the frame including the use request beknown to a transmission source of the frame including the use request.

(18)

A communication apparatus, including:

a communication unit configured to receive a frame of a first formatincluding a training signal and a frame of a second format not includinga first field which is at least a part of the training signal.

(19)

The communication apparatus according to (18), further including:

a processing unit configured to select one of the frame of the firstformat and the frame of the second format as a frame to be received, onthe basis of a use request included in a transmitted frame,

wherein the communication unit receives the frame of the selectedformat.

(20)

A communication method, including:

selecting one of a frame of a first format including a training signaland a frame of a second format not including a first field which is atleast a part of the training signal, and generating the frame of theselected format; and

transmitting the frame of the first format or the frame of the secondformat.

REFERENCE SIGNS LIST

-   10 communication apparatus-   11 data processing unit-   12 communication unit-   13 modulation/demodulation unit-   14 radio interface unit-   15 control unit-   16 signal processing unit

The invention claimed is:
 1. A communication apparatus comprisingcircuitry configured to: establish a communication link with a secondcommunication apparatus; determine whether or not the secondcommunication apparatus supports a very short physical layer convergenceprotocol (“VSP”); calculate a candidate time length for communicationswith the second communication apparatus; and transmit informationindicating the candidate time length to the second communicationapparatus in an exchange frame, wherein the candidate time lengthindicates an estimated range of a communication synchronization errorwith the second communication apparatus.
 2. The communication apparatusof claim 1; wherein the exchange frame comprises a header and a framebody.
 3. The communication apparatus of claim 2, wherein the exchangeframe further comprises a physical layer convergence protocol (PLCP). 4.The communication apparatus of claim 3, wherein the informationindicating the candidate time length is transmitted in the frame body.5. The communication apparatus of claim 4, wherein the informationindicating the candidate time length is configured with an actioncategory and an action identification.
 6. The communication apparatus ofclaim 1, wherein the circuitry is further configured to generate a framewith a first format when the candidate time length has not elapsed sincetransmission of a previous frame to the second communication apparatus.7. The communication apparatus of claim 6, wherein the first format isthe VSP.
 8. The communication apparatus of claim 6, wherein thecircuitry is further configured to generate the frame with a secondformat when the candidate time length has elapsed since transmission ofthe previous frame to the second communication apparatus.
 9. Thecommunication apparatus of claim 1, wherein the circuitry is furtherconfigured to: in a first case when it is determined that the secondcommunication apparatus does not support the VSP, turn off a VSPsetting.
 10. The communication apparatus of claim 9, wherein thecircuitry is further configured to: in a second case when it isdetermined that the second communication apparatus does support the VSP,turn on the VSP setting.
 11. A method of communication for acommunication apparatus, the method comprising: establishing acommunication link With a second communication apparatus; determiningwhether or not the second communication apparatus supports a very shortphysical layer convergence protocol (“VSP”); calculating a candidatetime length for communications with the second communication apparatus;and transmitting information indicating the candidate time length to thesecond communication apparatus in an exchange frame, wherein thecandidate time length indicates an estimated range of a communicationsynchronization error with the second communication apparatus.
 12. Themethod of claim 11, wherein the exchange frame comprises a header and aframe body.
 13. The method of claim 12, wherein the exchange framefurther comprises a physical layer convergence protocol (PLCP).
 14. Themethod of claim 13, wherein the information indicating the candidatetime length is transmitted in the frame body.
 15. The method of claim14, wherein the information, indicating the candidate time length isconfigured with an action category and an action identification.
 16. Themethod of claim 11, further comprising: in a first case when it isdetermined that the second communication apparatus does not support theVSP, turning off a VSP setting.
 17. The method of claim 16, furthercomprising: in a second case when it is determined that the secondcommunication apparatus does support the VSP, turning on the VSPsetting.
 18. The method of claim 11, further comprising generating aframe with a first format when the candidate time length has not elapsedsince transmission of a previous frame to the second communicationapparatus.
 19. The method of claim 18, wherein the first format is theVSP.
 20. The method of claim 18, further comprising generating the framewith a second format when the candidate time length has elapsed sincetransmission of the previous frame to the second communicationapparatus.